1. Field of the Invention
This invention relates to field of visual or non-contact inspection systems and methods. In this field, objects or parts of an object are visually scanned to produce profile images. The invention particularly relates to a system and method for gauging the thickness of a light-reflective, contoured object, such as a vehicle wheel, without destroying the object being gauged and without physically contacting said object in order to take any measurement readings thereof. The system and method of this invention may be used to gauge the thickness of a hot vehicle wheel, such as one recently removed from a forging press or tempering oven. The invention is designed for on-line inspection of various intermediates within the wheel manufacturing process but may also be positioned apart from the wheel manufacturing area. In any event, this system reduces scrap levels, eliminates the waste associated with processing pre-machined wheels which do not meet dimensional specifications and improves the ability to monitor manufacturing equipment for defects.
2. Technology Review
The field of contactless measuring has grown by leaps and bounds in recent years. Because of the accuracy and speed that various systems provide, contactless measuring methods are finding their way into more and more product manufacturing operations and/or post-manufacturing inspection stations.
In U.S. Pat. No. 4,674,869, there is claimed a method and apparatus for determining the contour of a varying contoured object surface. The method and apparatus employ optical triangulation-based coordinate measurement machines and robotic guidance of its light sensors to accurately measure such complex shapes as the teeth of a gear, or turbine blades.
U.S. Pat. No. 4,695,163 shows a method and apparatus for determining surface shapes using reflected laser light. This system incrementally moves a laser light source in a rectilinear path along a track, and pivotal about the track. Light reflected from the object's surface is maximally polarized when its angle of incidence equals Brewster's Angle. Information about the position of the light source is then fed to a computer which reconstructs the shape of the surface being scanned by plotting a two-dimensional view of the spatial points detected by this system's sensing means.
The non-contact gauging system set forth in U.S Pat. No. 4,798,469 employs a cone of light as its optical means to determine the relative locations of various features of an object, such as its size and shape. The system utilizes both incident and reflected light from a disc-like spot illuminated on the surface of the object being gauged. Preferred embodiments of this system include multiple gauge heads, all operated through a single microcomputer.
In U.S. Pat. No. 4,803,645, there is claimed a method and apparatus for measuring the coordinates of an object viewed from at least three different directions. The method of measuring object coordinates with this apparatus requires deriving correlations between the observed coordinates and those from a measured reference point.
U.S. Pat. No. 4,679,447 shows a method and apparatus for gauging railroad wheels for warping, rotundity and tape size. Although this apparatus may employ a plurality of lasers and receivers, the second and third lasers combine to measure the wheel's outside diameter at successive angular cross-sections and not across any sort of thickness plane through the wheel.
The method and apparatus for measuring the tread quality of a railroad wheel from U.S. Pat. No. 4,798,964 illuminates the wheel's circumference while the wheel remains on a railroad car passing over a particular measuring area of railroad track. The lasers and camera sensors of this system produce analog signals representing the wheel's quality of tread or profile. Such information is then digitized and supplied to a central processing unit for determining whether said wheel should be subjected to an automatic wheel truing operation.
Prior to the present invention, vehicle wheels had to be cooled to the point where they were safe to contact for manually measuring various cross-sectional thicknesses with known and other elaborate caliper gauging devices. Such devices often had to be adapted for taking readings of the wheel's contours, while themselves fitting over and about the wheel's various inner and outer surface contours. In some cases, precision of the measurements taken were sacrificed in order to obtain approximate thickness readings of certain wheel regions. Much time was lost waiting for the forged wheel blank to cool, then wrestling with taking multiple measurements thereof. During this time, literally hundreds of wheels would be forged with the same undetected processing error being passed on to each successive wheel. The wheel inspection system of this invention makes such prior measuring practices seem almost prehistoric by comparison.